Question about Direct Shear Test, CU and UU test

[icanhearringing]

I am reading a report about a slope failure due to a thin layer of clay being oversaturated and the engineering firm responsible for the investigation performed three different tests for analysis (direct shear, trixial CU and UU). My question is why would they perform these three different tests? Don't they all give the same shear strength parameters? (c, normal stress, friction angle)?

 

[EireChch]

UU only gives undrained strength only
shear box and CU give drained friction angle and drained c'.

Not unusual to do all 3 tests IMO.

 

[ripongeo]

UU gives undrained parameters on the other hand, CU and Direct shear give drained parameters (cohesion and Angle of internal friction). I think, Direct shear is not needed if CU conducted.